Dennis McClendon

Posted 10 December 2007 - 02:23 PM

Dennis McClendon

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I'm a little unclear whether shapefiles contain all the information needed to rescale and reproject them. Don't you often need more information (projection, units, datum, etc.) before you can get them to properly match up?

peanut

Posted 10 December 2007 - 02:34 PM

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I'm a little unclear whether shapefiles contain all the information needed to rescale and reproject them. Don't you often need more information (projection, units, datum, etc.) before you can get them to properly match up?

Usually shapefiles come with a projection file (.prj) which contains all of the projection information. Sometimes people neglect to include the projection file and then you have to track down which projection the actual data is in.

Rob

Posted 10 December 2007 - 03:24 PM

Sometimes, for quick and easy distribution, shapefiles are the way to go. Although, they tend to be messy (multiple files), and 'pieces' can get lost.

My personal preference is for personal geodatabases. You have one file (an mdb) that contains all of your information - metadata, attributes, projection information, etc.

At the GEOFi West regional level, we deal almost exclusively with personal geodatabases.

agree w/ all these points but the main drawback from using the PGDB for distribution is that only ESRI products can make use it. if the prj and xml files (metadata) are zipped with all the other files, it would provide the end user w/ a complete package for implementation/manipulation in most any software package.

Hans van der Maarel

Posted 10 December 2007 - 03:36 PM

My personal preference is for personal geodatabases. You have one file (an mdb) that contains all of your information - metadata, attributes, projection information, etc.

My (limited) experience with Personal Geodatabases is that they're not very easy to exchange with non-ESRI users. FME only supports them if you have Arc installed (at which point you don't need FME to read them...), Global Mapper doesn't support them at all, as far as I know. Manifold does (at least I've managed to do it succesfully, import the MDB and point to the field holding the geometry).

I know ESRI has a huge market share, but there's still people out there not using their products (like... eh... me!). I know Shape is an ESRI format as well, but it's so widely supported that one can easily consider it a de-facto standard. It's not 'open', but imho it doesn't have to be. If you have your data stored in shapefiles, there's plenty of options to get it out. If it's in a personal geodatabase, your options are somewhat limited (and options not starting with "Arc" are *very* limited). In essence, your data is locked up... Not as bad as some other formats: there's several Microstation add-ons that encrypt attribute data into a DGN file, really impossible to get it out of there, the geodata equivalent of a supermax... On that scale, personal geodatabase is more like electronic house-arrest...

Some things I don't like about shapefiles are the fact that you can only store one type of geometry per file, the fact it doesn't do texts and the fact that attribute names are limited to 10 uppercase characters. For those reasons, I personally prefer, just from a file structure point of view, the mid/mif format (even though that has its quirks when it comes to projections).

klacefield

Posted 10 December 2007 - 03:37 PM

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I agree with the Shapefile format as being the better format for sharing. Since it is an open standard format and can therefore be used in pretty much any GIS application, we post Shapefiles (including .prj & .shp.xml) of our county data along with posting the metadata online.

David T

Posted 11 December 2007 - 05:12 PM

My personal preference is for personal geodatabases. You have one file (an mdb) that contains all of your information - metadata, attributes, projection information, etc.

My (limited) experience with Personal Geodatabases is that they're not very easy to exchange with non-ESRI users.

Agreed. However, in my situation, it's fine. The Marine Corps uses ESRI GIS products as their enterprise solution. So, we're not concerned about non-ESRI users. If you're working with the USMC, you've got to give us back data in ESRI format. (Hence my preference for PGDB). (Just backing up my reasons why).

I'm a little unclear whether shapefiles contain all the information needed to rescale and reproject them. Don't you often need more information (projection, units, datum, etc.) before you can get them to properly match up?

Usually shapefiles come with a projection file (.prj) which contains all of the projection information. Sometimes people neglect to include the projection file and then you have to track down which projection the actual data is in.

"Usually" in terms of freshly generated .shp files from current versions of Arc. I still use a lot of older data, and it almost universally has no .prj file attached. Same is true for a lot of data from other non-Arc sources. Thank goodness for metadata.

To answer the original question, I like .shp files if for no other reason than that you don't have to worry about version or flavor. I have a lot of problems with them (add lack of spline curves to Hans's list), but of what's out there, they are the least painful...

Great points everyone. I would like to add, however, that it is also important to think about the actual needs of whoever you are sharing the data with, since this usually influences what GIS data type would best suit their needs. I love shapefiles and use them everyday, but their lack of topology make them not very friendly to edit, and often unsuitable for specific types of modeling/analysis. To be honest, I use coverages (old favorite), shapefiles AND GDB's. Which one I use depends on my current needs, and what the final needs of my client will be. For example, if I know that my client has THE SAME version of ArcGIS as I do (remember, gdb's are NOT backwards compatible... i learned this the hard way ), then I will happily build a GDB and use that for all of my editing, mapping, etc. However, if I'm sharing data with either a non-GIS saavy person, or someone who does not have the same version of ArcGIS as I do, I will always send them a zipped up shapefile with a .prj file and a description of how all the files (dbf, shx, shp etc) represent the shapefile and thus need to be stored in the same place. I know that this is diverging a little from your initial question Jessdpsu, but I think it's important that even though there are standards in place we still should consider compatibility issues and potential user needs when deciding on GIS data formats.